# Converting a PWM wave into pure DC

#### YASH VERMA

Mar 21, 2018
7
Hello all,

I want to convert a PWM wave into pure DC with DC value as the peak value of PWM wave. I have tried using a peak detector circuit which has a diode, a capacitor, and a resistor. Although, I am not getting strictly peak value of PWM as DC. I have also tried using a low pass filter with a smoothing capacitor, that also does not get me my result. I again do not get peak value of PWM signal.

Best regards,
Yash Verma

#### duke37

Jan 9, 2011
5,364
The diode and capacitor will give a value of the peak minus the diode voltage drop.
To get better than this, you will need an ideal diode which can be simulated with an op-amp but will need a higher voltage power supply to drive it.

A low pass filter will give the average voltage which is of course always less than the maximum.

Why do you want the peak voltage? This can be estimated from the applied voltage.

#### kellys_eye

Jun 25, 2010
6,514
Why do you want the peak voltage?
I was thinking the same - most queries of this type are looking for a DC voltage proportional to the PWM signal ratio....

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,889
I want to convert a PWM wave into pure DC with DC value as the peak value of PWM wave.
The peak value of PWM wave is CONSTANT. The only thing that varies is the pulse width, and possibly the pulse repetition frequency.

Please post either an oscilloscope screen-capture of your "PWM wave," or a hand-drawn sketch showing what kind of wave you want to "convert into pure DC." Your question does not make any sense.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510

I would suggest that you look at the power supply to the PWM controller. It will be DC having a value equal to the peak value of the PWM output.

#### YASH VERMA

Mar 21, 2018
7
The diode and capacitor will give a value of the peak minus the diode voltage drop.
To get better than this, you will need an ideal diode which can be simulated with an op-amp but will need a higher voltage power supply to drive it.

A low pass filter will give the average voltage which is of course always less than the maximum.

Why do you want the peak voltage? This can be estimated from the applied voltage.

I am actually trying to amplify a PWM signal which in some mVolts to some volts by a gain factor of 38. I have a big circuit with a common supply and this supply is supposed to vary from 8 to 16 Volts. So i want the peak of the amplified PWM signal.

#### duke37

Jan 9, 2011
5,364
You can look up Wikipedia "Precision rectifier". The article is taken from Horowitz and Hill "The art of electronics".

I still do not understand what you want. The PWM signal is used to vary the average output voltage. The signal should be sufficient to turn on the switching transistors , say 10 to 20 Volts and the exact level of this will not affect the output voltage.

Please show us a schematic of what you have.

#### BobK

Jan 5, 2010
7,682
Why would you want to follow the peak voltage? The signal in a PWM signal is not the peak voltage (which typically would remain constant), the signal is in the duty cycle. If you have reproduced the duty cycle at a higher voltage, you have reproduced the PWM signal.

Perhaps you are using the term PWM incorrectly.

Bob

Jun 21, 2012
4,889

Replies
7
Views
2K
Replies
10
Views
10K
J
Replies
1
Views
1K
B
I
Replies
1
Views
3K
Andrew Holme
A
Replies
4
Views
369